1. Technical Field
The present invention relates to a signal processing apparatus for processing an image pickup signal including two or more kinds of color signals and luminance signals which are respectively output from image pickup elements.
2. Related Art
In an image sensor of a single plate type having a color filter of a Bayer matrix, since only one color component signal can be obtained from each of a large number of photoelectric conversion elements included in the image sensor, it is necessary to carry out a so called synchronizing processing in which, at pixel positions that correspond to the respective ones of the large number of photoelectric conversion elements, there are interpolated the color signals that cannot be obtained from these photoelectric conversion elements. The synchronizing processing is a processing which interpolates color signals originally not existing at the pixel positions using color signals existing around such pixel positions and, therefore, there is a possibility that a false color can occur. In the patent reference 1 (JP-A-2001-101398), there is disclosed a method which can reduce the false color whatever the color may be.
FIG. 5 is a view of the arrangement of color signals which are obtained from a single plate type of image sensor having a color filter of a Bayer arrangement.
Circles shown in FIG. 5 express color signals respectively: specifically, a circle with “R” stated therein expresses a red color signal; a circle with “G” stated therein expresses a green color signal; and, a circle with “BB” stated therein expresses a blue color signal. On the respective color signals, there are given numbers (01˜16) which express pixel positions respectively.
When enforcing a synchronizing processing on such image pickup signals as shown in FIG. 5 using a method disclosed in the patent reference 1, the calculation of an R signal (R10) to be interpolated at an pixel position 10 of a 0 signal in a line of B and G signals is carried out according to the operation of R10=G10+(R09−G09) based on the premise that, when an object is assumed to have a correlation in the vertical direction, differences between R signals and 0 signals in the local area of an image are equal to each other, that is, based on the premise that there holds the relationship, R10−G10=R09−G09. In this case, a 0 signal (G09) at an R09 pixel position is calculated by enforcing a one-dimensional interpolation calculation on a G signal on an RG line where the R09 pixel position 09 exists, for example, G09=(G05+G13)/2.
In this manner, a color signal (for example, R10) to be interpolated at an arbitrary pixel position (for example, a pixel position 10) is estimated using (i) a G signal (G10) existing at the arbitrary pixel position, (ii) a color signal (R09) which is of the same kind as the color signal to be interpolated and exists at an adjacent pixel position included in a line adjoining a line including the arbitrary pixel portion, and (iii) G signals (G05, G13) respectively existing in the vicinity of the same kind of color signal, thereby reducing the occurrence of the false color effectively.
However, according to the method disclosed in the patent reference 1, when much noise is included in signals G10, G05 and G13, much noise is also included in a signal R10 which is generated using these signals, resulting in the deteriorated image. Also, depending on the colors of an object, a correlation between the R and G signals can be lowered, which can decrease the false color reduction effect. Further, when an object has a correlation in an oblique direction, the signals G and RB lines are arranged alternately and, therefore, the false color reduction effect cannot be expected in a correlation calculation using the G signals.
The present invention aims at solving the above problems found in the above signal processing method. Thus, it is an object of the invention to provide a signal processing apparatus which can enforce a color signal interpolating processing (a synchronizing processing) for reduction of a false color and noise on any signal.